Although he admitted some defeat while announcing Tumblr's very first ad units in April 2012 — "I was probably being an idiot then," Karp said — he has done a complete 180 since selling the social platform to a very ad-friendly Yahoo for $1.1 billion.

Advertisers' biggest and swankiest festival, the Cannes Lions, is taking place this week, and Karp is there wooing potential partners.

Ad Age reports, "Words like "humbled," "privileged," and "honored" tripped off his tongue, as did the hope that next year the crowd would be winning Lions for work created on Tumblr."

Karp also stated to the audience, "You guys are more talented than any one in the Tumblr office or in Palo Alto or Sunnyvale. We're constantly in awe, constantly in service."